Image forming apparatus with corona discharge device for transferring toner image

Abstract

An image forming apparatus has a corona discharge device for transferring a toner image formed on a photosensitive member onto paper and a suction fan for drawing air from the inside of the corona discharge device to exhaust ozone. The corona discharge device has a wire electrode, a shield member surrounding the wire electrode including a lower portion located on the opposite side to the photosensitive member with respect to the wire electrode and a pair of side portions extending from the respective side edges of the lower portion toward the photosensitive member, and a cover member located between the photosensitive member and the wire electrode and extending downstream from the upstream side of the wire electrode with respect to the direction of transport of the paper to cover a part of the upper side of the wire electrode, the remaining part of the upper side of the wire electrode being used for transferring the toner image by corona discharge. The shield member is formed with a first opening in the lower portion for drawing air therethrough, and a second opening in one of the side portions at a position near the photosensitive member. With the above arrangement, air flows through the remaining part of the upper side of the wire electrode and also through the second opening into the corona discharge device and then flows out through the first opening by being drawn by the suction fan.

What is claimed is: 
     
       1. An image forming apparatus for transferring a toner image onto a paper transported in a paper transport direction, comprising: a tone image carrier for carrying a toner image thereon;   a corona discharge device for transferring a toner image from said toner image carrier to a paper, said corona discharge device comprising: a wire electrode disposed adjacent said toner image carrier such that said toner image carrier is on one side of said wire electrode,   a shield member surrounding said wire electrode, said shield member including a lower portion disposed on the side of said wire electrode opposite said toner image carrier and a pair of side portions extending from respective side edges of said lower portion toward said toner image carrier, and said shield member having a first opening in said lower portion, a second opening in one of said side portions adjacent said toner image carrier, and an open space facing said toner image carrier, and   a cover member between said wire electrode and said toner image carrier, said cover member extending downstream from the upstream side of said wire electrode with respect to the direction of transport of the paper to cover a first part of said open space of said shield member to partially block said wire electrode from the toner image carrier while leaving a second part of said open space open for corona discharge by said wire electrode for transferring a toner image from said toner image carrier to a paper; and     means for sucking air from the interior space of said shield member connected to said first opening for sucking air therethrough and causing outside air to flow into the interior space of said shield member through said second opening and said second part of said open space of said shield member.   
     
     
       2. The image forming apparatus as set forth in claim 1, wherein said second opening in one of said side portions of said shield member is located, from the upper edge of said side portion adjacent said toner image carrier, within one fourth the distance from said upper edge of said side portion to said lower portion. 
     
     
       3. The image forming apparatus as set forth in claim 1, wherein said cover member extends from the upper end of one of said side portions to cover said first part of said open space and partially block said wire electrode from said toner image carrier. 
     
     
       4. The image forming apparatus as set forth in claim 1, and further comprising: a guide member disposed upstream of said corona discharge device with respect to the direction of transport of paper for guiding paper to a transfer region between said corona discharge device and said toner image carrier, wherein said cover member is attached to said guide member.   
     
     
       5. The image forming apparatus as set forth in claim 4, wherein: said second opening in one of said side portions is bounded by said guide member and said side portion.   
     
     
       6. The image forming apparatus as set forth in claim 5, wherein said second opening in one of said side portions of said shield member is located, from the upper edge of said side portion adjacent said toner image carrier, within one fourth the distance from said upper edge of said side portion to said lower portion. 
     
     
       7. An image forming apparatus for transferring a toner image from a photosensitive drum onto paper transported in a direction of transport, comprising: a corona discharge device for transferring a toner image on the photosensitive drum onto paper, said corona discharge device comprising: a wire electrode to be disposed so as to extend in the axial direction of the photosensitive drum, and   a stabilizer plate surrounding said wire electrode,e comprising a first side portion upstream of said wire electrode with respect to the direction of transport of paper covering said wire electrode on a first side thereof, a second side portion downstream of said wire electrode covering said wire electrode on a second side thereof, a third portion interconnecting said first and second portios at first ends thereof and covering said wire electrode at a third side thereof, and a fourth portion extending from a second end of said first side portion and partially covering said wire electrode on a fourth side thereof, a first opening disposed in said third portion, and a second opening disposed in said first side portion so as to be in proximity to the photosensitive drum, said second side portion and said fourth portion defining a discharge opening therebetween for corona discharge for transferring a toner image; and     means for sucking air from the interior of said stabilizer plate out through said first opening, causing air to flow into said stabilizer plate from the outside through said second opening and through said discharge opening.   
     
     
       8. The image forming apparatus as set forth in claim 7, wherein: said second opening in said first side portion is located, from said second end of said side portion, within one-fourth the distance from said second end to said first end.   
     
     
       9. An image forming apparatus for transferring a toner image from a photosensitive drum onto a paper transported in a direction of transport, comprising: a corona discharge device for transferring a toner image on the photosensitive drum onto paper, said corona discharge device comprising: a wire electrode to be disposed so as to extend in the axial direction of the photosensitive drum, and   a stabilizer plate surrounding said wire electrode, comprising a first side portion upstream of said wire electrode with respect to the direction of transport of paper covering said wire electrode on a first side thereof, a second side portion downstream of said wire electrode covering said wire electrode on a second side thereof, and a third portion interconnecting said first and second portions at first ends thereof and covering said wire electrode at a third side thereof, said third portion having a first opening therein;     a guide member upstream of said corona discharge device with respect to the direction of transport of paper for guiding paper to a transfer region between said corona discharge device and the photosensitive drum;   a cover member attached to said guide member and extending downstream from the upstream side of said wire electrode to partly cover said wire electrode,e said cover member and said first portion defining a second opening therebetween to be disposed in proximity to the photosensitive drum, and said cover member and said second side portion defining a discharge opening therebetween for corona discharge for transferring a toner image; and   means for sucking air from the interior of said stabilizer plate out through said first opening, causing air to flow into said stabilizer plate from the outside through said second opening and through said discharge opening.   
     
     
       10. The image forming apparatus as set forth in claim 9, wherein: said second opening is located, from said cover member, within one-fourth the distance from said cover member to said first end of said side portion.   
     
     
       11. An image forming apparatus for transferring a toner image by corona discharge onto paper transported in a paper transport direction, comprising: a photosensitive member for having a toner image formed thereon;   a corona discharge means confrontingly disposed with respect to said photosensitive member for transferring a toner image from said photosensitive member onto a paper, said corona discharge means comprising: (a) electrode means for generating corona ions,   (b) shield means for encompassing said electrode means about three sides thereof with first, second and third shield means portions, and having a fourth open portion for exposing said photosensitive member to and confronting said photosensitive member with said electrode means,   (c) a first opening in said first portion, wherein said first portion is disposed opposite said fourth portion;   (d) a second opening in said second portion, wherein said second portion is disposed opposite to and upstream of said third portion with respect to the paper transport direction, and   (e) a cover member located at said fourth portion and extending from the upstream side thereof for partially shielding said fourth portion; and     means for sucking air to cause air to flow out of and into said shield means through said first and second openings.   
     
     
       12. The image forming apparatus as set forth in claim 11, wherein: said second opening is located, from said cover member, within one-fourth the distance from said cover member to the opposite end of said second portion.   
     
     
       13. The image forming apparatus as set forth in claim 12, and further comprising: a guide member upstream of said corona discharge device for guiding paper to a transfer region between said corona discharge device and said photosensitive member, wherein said cover member is attached to said guide member.